Let's just dive right in. I start my analysis of yesterday's voting across 12 states in Nevada, because what happened there last night sets up what is certain to be one of the most-watched contests of November.

The Democratic incumbent will be Harry Reid, the Senate majority leader. And yesterday GOP voters decided to nominate the right-most of three candidates, Sharron Angle, who was the Tea Party movement's preferred candidate. Reid had trailed in polls against all three Republican contenders for a long time, probably as a result of the state's economy and the role he played in passing the healthcare bill, which wasn't popular in this purple state that Barack Obama narrowly carried in 2008.

Reid shouldn't be smug. He leads Angle only by about six points and he's under 50%. And he's charged with running the Democrats' national agenda in the Senate, which might not always be so popular in his home state. This will be one of the top races in the country this fall, maybe the most closely watched one of all.

The second-biggest story from yesterday is out of Arkansas, where Blanche Lincoln held on to defeat an intra-party challenge from Bill Halter. National unions threw $10m at defeating Lincoln, a centrist-conservative Democrat, and a Halter victory was widely expected as of yesterday afternoon. But Lincoln won by four points.

Bill Clinton came into his old state hard for Lincoln, and the incumbent also touted her support from Obama. The liberal blogosphere raised millions for Halter. Between those activists and the unions, Lincoln was able to argue that outsiders were trying to take over the state, a trope that often works in American politics. This was a big loss for the unions and it demonstrated that populist anger on the left is no match for the populist anger on the right.

Lincoln's celebration may be short-lived. She's well behind the man who'll be her Republican opponent this fall, nearly 20 points. She's never lost a general election, so she shouldn't be counted out, but this is a seat that seems likely to go Republican.

Sarah Palin-endorsed Nikki Haley led the voting in the South Carolina GOP gubernatorial primary but fell just short of the 50% needed to avoid a runoff, so she'll face a conservative congressman in two weeks. It would appear she'll win, unless some of the gymnastic allegations about her private life are proven to be true. There are very few national ramifications here, though. South Carolina is likely to have a conservative Republican governor. Shocking.

Things could be different in California, though. Meg Whitman v Jerry Brown is going to be a fascinating governor's race, and Barbara Boxer v Carly Fiorina will almost surely be a $100m Senate race at the very least. The Democrats held modest leads as of this mid-May poll, with Boxer nine points up on Fiorina and Brown just four points ahead of Whitman.

I'd pick Boxer to hold on. She's a tough campaigner who's been supposedly on the ropes before, and Fiorina moved hard to the right to win the primary, running an Arizona-style campaign in a state that's more liberal than that. Whitman v Brown strikes me as tougher to call. Brown seems to remain popular in the state, but Whitman should be able to exploit that Brown has been around so long (since the 1970s) and is arguably too old (72) to be an energetic (or even awake) governor for eight years.

One doubts unless something really weird happens that the state will be in play in 2012. But even short of that, a California governor is a national player, so Whitman would be a figure of influence in her party if she made it to Sacramento. Of course, she'll be a little busy trying to fix probably the biggest state fiscal mess in the country.

One House of Representatives contest I'll single out is Virginia 5, which stands out among those districts contested last night as one that will definitely be a bellwether race in November. The incumbent is Democrat Tom Perriello, who is just in his first term and won in 2008 on the strength of anti-Bush backlash in the district, which generally leans Republican.

Establishment Republican Bob Hunt easily fended off more rightwing challengers last night. But he was hammered in the primary by opponents on the right who said he's too moderate. A Tea Party activist has vowed to run on a third-party line if Hunt won, and that activist could receive the backing of Hunt's most prominent conservative primary opponent, a real-estate developer who scored 26% of the vote last night.

In other words, this sets up a situation where the national GOP may decide to come in and chase the Tea Party person out of the race (egads, maybe even with the promise of some kind of job). If that quarrel unfolds, it will be well worth watching. And if the Tea Party person stays in the race, he likely hands a very unexpected victory to Perriello.

The big electoral mystery of this year in the US will be whether the tea party movement was boon or bane to the GOP. Nevada and Virginia 5 (if there's a third-party candidacy) will go a long way toward helping us answer that question.